1. Field of the Invention
The present invention relates to a plane circular polarization antenna and an electronic apparatus.
2. Description of the Related Art
Conventionally, antennas of portable terminals such as a portable phone and a personal digital assistant (PDA) for wireless communication have been decreased in size. For example, a film antenna is proposed which has an antenna pattern on a planar film and radiates single polarization (for example, Japanese Patent No. 3656610 and Japanese Patent No. 3622959). Also, a film antenna which radiates vertical polarization and horizontal polarization simultaneously is proposed (for example, Japanese Patent No. 3830358). The above film antennas are based on an inverted F antenna having moderate directional characteristics.
A film antenna is also proposed which produces a circular polarization using a modified loop antenna.
The conventional film antenna which radiates single polarization can radiate only single polarization. Thus, when the conventional film antenna is applied to mobile communication (in particular, a portable communication apparatus such as a handy terminal), the mobile communication may become unstable and may be disrupted depending on orientation of the antenna. Therefore, transmitting polarization needs to match receiving polarization.
The conventional film type inverted F plane antenna which radiates vertical and horizontal polarization cannot make phase difference between elements, therefore, it is not possible to radiate circular polarization.
The conventional film antenna which produces circular polarization using the loop antenna is large in shape and is difficult to be mounted to a small portable apparatus. Such film antenna also has a significant directivity. Therefore, depending on the orientation of the antenna, a radio wave cannot be radiated at many angles and communication may be disrupted. Thus, the film antenna is unsuitable for mobile communication between portable apparatuses.
Furthermore, when the film antenna which produces the circular polarization using the loop antenna is mounted close to a ground plane, the antenna comes to deviate from resonance and not to function. Accordingly, a position to which the film antenna is mounted is significantly limited.